Physiology 206 Lecture 4 Outline of Last Lecture I Osmosis II Van t Hof III Osmolarity IV Nervous System V Classify Neurons Outline of Current Lecture I Neurons II Glia cells III Action potentials IV Voltage Gated Ion channels Current Lecture 1 22 14 Sensory afferent in Motor efferent out Interneurons transmit information between sensory and motor neurons Glia cells glia glue o Oligodendroglia wrap around axons of neurons in CNS and insulate them Multiple branches that wrap around one neuron Forms myelin sheath in CNS o Schwann cells one Schwann cell wraps around one axons and insulates it from other axons and extracellular fluid ECF Forms myelin sheath in PNS o Astroglia looks like stars has cell body with many projections Some terminate on cell body of a neuron some on the surface of a capillary Form bridge between neurons and capillaries These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Facilitate transfer of materials between the two Neuron capillary carries waste Capillary neuron carries nutrients o Microglia very small not very many When there s an injury microglia accumulate at the site of injury Potential o Potential voltage o Driving force that makes charges move o Exist where there are unequal amounts of charge o Unequal distribution of ions across membranes o When charges move voltage IN OUT K k Na Na The differences between in and out are the differences in concentration of charges 2 factors that affect action potential o Greater concentration difference greater potential o The mobility of particles ions across membranes Net voltage total across membrane potential The sum of charges moving add up all the ions Voltage across the cell membrane is such that if the inside of the cell is negative then the outside of the cell is positive Lskrjl Resting potential 75mV o the absolute value of the resting potential is never really known we would have to put electrodes inside and outside the cell to measure the ion concentration we can t do this because it causes the ions to leak punch holes in cell membrane when testing so whenever we test it isn t exactly accurate o microelectrodes used to measure membrane potentials the smaller the electrode the more accurate the reading If you continuously increase the graded stimulus the membrane potential will go to zero then return to normal o once you reach a threshold value the responses will always be the same o get an all or nothing response if the threshold value is reached there will be an action potential o graded potentials stay within soma o action potentials exit the soma and travel along the axon In the milliseconds after the action potential has been stimulated another action potential can t be stimulated this is called the refractory period o Relevant refractory period at the end of the refractory period the action potential can be stimulated during this time o Duration of refractory period sets a standard of how many action potentials can be generated Sets an upper limit on the frequency of the action potentials Cell membranes have ion channels through which ions can pass o Can be closed or open Voltage Gated Channels 50mV o Closed in resting state ions can only cross membrane slowly Ion concentration difference is large Membrane potential is small o Open ions can easily cross the membrane Ion concentration difference small Membrane potential 0 o When the voltage across the membrane is greater than 50mV the channels are closed o When the voltage across the membrane is less than 50mV the channels are open pass the threshold value